The present invention relates to mechanical face seals and in particular to mechanical face seals which are subject to fluid pressure both internally and externally.
In mechanical face seals which are subject to, for example, a fluid product under pressure on one side and a fluid sealant under pressure on the other side, it is necessary to seal the axially moveable seal face member to its associated component in a manner which will provide a seal between the product and sealant regardless of which is at higher pressure. This may be achieved by providing an O-ring in a groove defined between the seal face member and its associated component, so that if the pressure of the product is higher, the O-ring will be forced into sealing engagement with one wall of the groove, whereas if the pressure of the sealant is higher, the O-ring will be forced into engagement with the other wall of the groove. With this arrangement, it is necessary to reduce the clearance between the seal face member and associated component in order to minimise extrusion of the O-ring.
If the product contains particulate material, there is a possibility that the small gap between the seal face member and associated component on the product side of the O-ring may become clogged, preventing free axial movement of the seal face member, so that as the seal faces wear the seal will leak.